Grammatically an emdash is fine in most places a comma is fine. It adds a bit more emphasis to the bit after the dash.

I went to the grocery store, and bought tomatoes.

I went to the grocery store---and bought a Ferrari.

The second one has a bit more of a dramatic pause.

"Eats, Shoots, and Leaves" is a fun book with a great chapter about the dash with many good examples.

Emdashes and commas aren't interchangeable, and your example there demonstrates one great reason why. The emdash establishes a discontinuity rather than one thing flowing into another, which is why the tomatoes don't merit one but the Ferrari does: you are using the emdash to emphasize the situational irony.

Going back to Anthropic's post:

> They’re the world’s most advanced models for coding and knowledge work---and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress.

The first thing directly implies and flows smoothly into the next---or would, if not for the awkward emdash. There is no discontinuity, no twist or shift in context, no implied question and provided answer, no punchline. It's just distracting.

Your first example shouldn't have a comma at all.

Em dashes are commonly used to add emphasis, even where you would ordinarily use a comma. Their flexibility is why many people love them! See https://www.merriam-webster.com/grammar/em-dash-en-dash-how-...

Yes, I know what an emdash is---I've been using them in my writing since long before they came to the fore of the AI writing conversation. Anthropic's use of the emdash in the fragment I quoted is clumsy and reads poorly relative to the obvious alternative, a comma.

I didn’t mean to suggest you don’t know what an em dash is. But you said “this isn’t how you use them.” And my response is: actually, this use of them is totally fine.

Well, I disagree! https://news.ycombinator.com/item?id=49527581

It's fine in the sense that when a bad writer writes something I can usually understand what they're trying to say.

I love em dashes because they are kind of a wildcard. When I read this same sentence, I interpret this emdash as an ellipses and not a comma.

Language is use :)

it got want to use em dash. but decide: do? q is if appropriate. check martian websner blog. verdict yes---emdash + comma interchangeable---proceed---judgment superficial however no desire dig deeper style irrelevant effect on reader irrelevant meter and rhythm irrelevant restate equivalence with comma established::chain unbroken::consider semicolon? consider ellipsis consider comma consider sentence break all no. preference for emdash est fiat. and all nail shapeds are for hammering.